In performing any one of several useful types of analyses, microfluidic devices may be employed. Whether applied for the purpose of DNA separation or drug screening, the ability to achieve movement of sample, reagents and buffer within a network of fine trenches or channels can result is great time savings over conventional techniques. Most all common laboratory procedures such as mixing, incubation, metering, dilution, purification, capture, concentration, injection, separation, and detection may be performed on a single microfluidic “chip.” What is more, the chip format allows for parallel tasking and concomitant gains in productivity.
Data from experiments run on microfluidic devices is commonly extracted utilizing optical detection techniques. Laser-induced fluorescence (LIF) techniques are particularly advantageous. LIF techniques employ laser light to excite material for detection by an optical unit such as a photomultiplier tube (PMT) device or charge-coupled device (CCD) camera. One or more PMT devices or CCD cameras may be used or any combination thereof.
Most often, LIF detection utilizes a laser beam directed normal to the plane of the microfabricated device, exciting molecules at or adjacent to a detection zone. Another detection scheme employs light reflecting structures integrated within a chip to direct a beam across a detection zone. Such an approach may further utilize a second reflector to allow light detection normal to the plane of the microfluidic device.
Irrespective of what advantages such systems provide, they suffer from serious drawbacks. Background illumination or scattering of light introduced at detection windows and less-than-perfect reflecting surfaces often adversely affect sample detection capabilities. Furthermore, for some configurations, the layout will require passing the laser light through the material forming the body or a cover of the microfluidic device. Some configurations impose difficult demands on chip flatness or dimensional tolerances. This may introduce background fluorescence (i.e., autofluorescence) that also decreases detection signal accuracy. More particularly, autofluorescence is the fluorescence generated by the microfluidic device material (e.g., the channel-wall material) upon illumination with the excitation beam. Again, autofluorescence is problematic because it decreases detection sensitivity.
Some have sought to address these problems through material choice to reduce background fluorescence and by use of high-quality optical surfaces to avoid light scattering within chips. Issues associated with cost and reproducibility are presented in either case. The present invention offers an elegant alternative in dealing with either fluorescence or optical challenges.
Further advantages and utility of the present invention may also be apparent to those with skill in the art upon further consideration of the various features of the present invention.